1. Field of the Invention
The present invention relates to a heating device made of ceramics, and more specifically, relates to a heating device for heating a wafer to be used as a substrate in a manufacturing process of a semiconductor device or heating other plate-like heating objects.
2. Description of the Related Art
In a manufacturing process of a semiconductor device, which uses a semiconductor manufacturing apparatus, heating treatment is implemented for forming an oxide film and the like on a wafer. As the heating device for heating the wafer, there is a heating device that includes a disc-like ceramic base having a heating surface opposite to the wafer as a heating object, in which a resistance heating element is embedded in the ceramic base. This heating device is suitable not only for a deposition apparatus in the manufacturing process of the semiconductor device but also advantageously for a surface treatment apparatus that performs dry etching for a surface of the heating object, and the like.
There is a heating device that further includes a support member for supporting the ceramic base, in which the support member is bonded to the ceramic base. This support member has a substantially cylindrical shape, in which one end surface is fixedly attached to an opposite surface of the ceramic base with the heating surface, that is, to a back surface thereof by solid-phase bonding or liquid-phase bonding.
With regard to such an attachment structure of the ceramic base and the support member, there is a heating device in which a rounded portion is provided between a bonding surface of the ceramic base and an outer circumferential surface of the support member (Japanese Patent Laid-Open Publication No. 2004-247745).
In such a conventional ceramic heater of Japanese Patent Laid-Open Publication No. 2004-247745 mentioned above, the back surface of the ceramic base and the outer circumferential surface of the support member are connected smoothly to each other by a curved surface of the rounded portion formed on a bonded portion between both thereof. An occurrence of a crack is suppressed by this rounded portion. However, the crack has sometimes occurred from the rounded portion concerned even if the rounded portion is present. When the crack occurs, there has been an apprehension that a thermal stress caused by heating and cooling the ceramic base at the time of using the heating device may be concentrated on a portion where the crack has occurred, whereby expansion of the crack may be brought.
In this connection, it is an object of the present invention to provide a heating device that effectively prevents the crack from occurring in the vicinity of the bonded portion between the ceramic base and the support member, thus making it possible to enhance reliability of the heating device concerned.